African Violets and Gesneriads: Rust?

Not sure what it is called. Rusty color on leaves. This only happens on my Chicago Flair plants. Just lost another one. It was huge and beautiful, then, this happened. Never has happened to another plant. What is the cause?

No, nothing changed.. No pictures... should have taken one. Looks like rust on the outer edge of the leaves. Starts outside, then one by one, takes over. Then dies. I just want to trash it fast when it gets bad. Just on the Chicago Flair. It always grows great for me, then later, this happens. From perfect to dead. :(

No, none of the pictures look like this. Wish I had a picture. It look like rust, orangey brown on the edges. Oldest leaves, and moves in to the young leaves. I have looked everywhere. I love Chicago Flair, but I can't get another! Keeps happening.

Anything is possible. Just so odd it never happens on any other variety. Out of ALL of the plants. They all get the same Semi Hydro, same everything. This happened in "soil" also. No specific grower either. Oh well. So odd!